In a wireless network, a wireless device may communicate with one or more radio network nodes to transmit and receive voice traffic, data traffic, control signals, and so on. Reference signals, or pilot signals, may be transmitted in communication systems to provide a phase reference that a receiver can use to synchronize timing of a transmission and adjust for frequency error between a transmitter and receiver. Reference signals may also provide a phase reference such that a receiver can estimate a propagation channel between a transmitter and the receiver to demodulate and decode a transmitted data message.
In cellular systems, reference signals transmitted in a cell from a base station to user equipment (UE) may be referred to as common or dedicated reference signals. Common, or cell-specific, reference signals (CRS) may be used by all UEs communicating with the cell and are typically broadcast with equal power in all directions within the cell. Dedicated, or user-specific, reference signals are typically received and used by a single user.
Machine-to-machine (M2M) communication (also referred to as machine type communication (MTC)) establishes communication between machines and/or between machines and humans. The communications may comprise exchange of data, signaling, measurement data, configuration information, etc. The device size may vary from that of a wallet to that of a base station. M2M devices are often used for applications like sensing environmental conditions (e.g., temperature reading, etc.), metering or measurement (e.g., electricity usage, etc.), fault finding or error detection, etc.
Generally MTC devices are low cost and low complexity. A low complexity UE that may be used for M2M operation may implement one or more low cost features, such as smaller downlink and uplink maximum transport block size (e.g., 1000 bits) and/or reduced downlink channel bandwidth of 1.4 MHz for data channel (e.g., PDSCH). A low cost UE may also comprise of a half-duplex (HD-FDD) and one or more of the following additional features: single receiver (1 Rx) at the UE, smaller downlink and/or uplink maximum transport block size (e.g., 1000 bits), and reduced downlink channel bandwidth of 1.4 MHz for data channel. The low cost UE may also be referred to as a low complexity UE.
Path loss between an M2M device and a base station can be large in some scenarios. For example, path loss may be large for an M2M device in a remote location (such as an M2M sensor or metering device located in the basement of a building). In such scenarios receiving a signal, including reference signals, from the base station may be challenging. For example, the path loss can be 20 dB worse than normal operation. Enhanced coverage in uplink and downlink may alleviate such challenges. Examples of techniques in the UE and/or in the radio network node for enhancing the coverage include transmit power boosting, repetition of transmitted signal, applying additional redundancy to the transmitted signal, use of advanced/enhanced receiver, etc. In general, when employing coverage enhancing techniques, the M2M may be referred to as operating in “coverage enhancing mode.” A low complexity UE (e.g., UE with one receiver) may also be capable of supporting enhanced coverage mode of operation.